1. Field of the Invention
The present invention relates to an abnormality diagnosis device in an exhaust heat recovery equipment which is used for a vehicle.
2. Description of Related Art
Recent years, various technologies, which recover exhaust heat from an exhaust system of an engine of a vehicle to use the exhaust heat for promotion of warm-up, for example, are proposed. An exhaust heat recovery equipment using a principle of a heat pipe is known as such a technology. A technology which disposes an evaporation part of a heat pipe in an engine exhaust pipe and disposes a condensation part of the heat pipe in a coolant passage of an engine, to heat engine coolant by exhaust heat, is disclosed in, for example, JP-A-2007-332857. More specifically, working fluid is enclosed in a circulating path that connects the evaporation part and the condensation part of the heat pipe. The working fluid is evaporated using heat from the outside in the evaporation part, and heat exchange is performed between the evaporated working fluid and engine coolant from the outside in the condensation part.
Furthermore, in JP-A-2007-332857, a valve is provided in the circulating path of the exhaust heat recovery equipment. Engine coolant temperature is increased using the exhaust heat or overheat is curbed by opening and closing the valve. More specifically, when the engine coolant temperature needs to be increased, such as at the time of engine starting, for example, the valve is opened to circulate the working fluid in the circulating path, and the engine coolant temperature is increased using the exhaust heat. When the engine coolant temperature does not need to be increased, such as after the warm-up of the engine, the valve is closed to accumulate the working fluid in the circulating path, thereby inhibiting the rise of the engine coolant temperature by the exhaust heat.
However, in an exhaust heat recovery equipment having a valve in the circulating path, if the valve fails for some reasons, the valve cannot be opened or closed in accordance with the engine coolant temperature. Accordingly, it is envisaged, for example, that exhaust heat cannot be used for temperature rising of engine coolant when an engine is not yet warmed up or that the exhaust heat is excessively supplied to the engine coolant after the completion of engine warm-up, so as to generate overheat.